1. Field of the Invention
The present invention relates to a variable focus lens, more particularly, which can be easily fabricated to prevent bubble formation with a protrusion formed at an opened end of a chamber.
2. Description of the Related Art
In general, a camera is equipped with a plurality of lenses, and designed to drive the lenses respectively in order to vary relative distances thereof, thereby adjusting its optical focal length. Owing to the miniaturization of optical devices such as a camera, demand for the miniaturization of a lens equipped therein is also on the rise.
As an approach to meet the miniaturization demand, a variable focus lens disclosed in WO 03/069380 was proposed.
FIG. 1 is a schematic cross-sectional view of a variable focus lens proposed as an embodiment of WO 03/069380.
As shown in FIG. 1, the variable focus lens includes a fluid chamber 5 having a cylinder wall to contain non-miscible first and second fluids A and B therein and a fluid contact layer 10 arranged on the inside of the cylinder wall. The first and second fluids A and B are in contact over a meniscus 14 and have different refractive indices. The variable focus lens also includes a first electrode 2 separated from the first and second fluids A and B by the fluid contact layer 10 and a second electrode 12 acting on the second fluid.
The first electrode 2 is a cylinder in shaped, formed from a metallic material, and coated by an insulating layer 8. The second electrode 12 is arranged at one end of the fluid chamber 5.
The fluid chamber 5 is covered or sealed by transparent front and back elements 4 and 6 to contain the first and second fluids A and B.
A sealing (shown in FIG. 4 and given with reference number 16) is also provided to hermetically couple the transparent front element 4 with the fluid contact layer 10.
The variable focus lens of this construction will operate as follows.
When no voltage is applied between the first electrode 2 and the second electrode 12, the fluid contact layer 10 has a higher wettablity with respect to the first fluid A than the second fluid B.
Due to electro-wetting, the wettability by the second fluid B varies under the application of a voltage between the first and second electrodes 2 and 12, which tends to change the contact angle of the meniscus 10 as indicated with Q1, Q2 and Q3.
The shape of the meniscus is thus variable in dependence on the applied voltage, which in turn achieves focus adjustment of the lens.
That is, as shown in FIGS. 1 to 3, according to the magnitude of the voltage applied, the angle of the meniscus 14 and the fluid contact layer 10 measured in the side of the first fluid B changes from an obtuse angle to an acute angle gradually, for example, in the order of 140, 100° and 60°.
Herein, FIG. 1 shows a lens configuration when lower voltage is applied, FIG. 2 shows a lens configuration where intermediate power is applied, and FIG. 3 shows a lens configuration where high voltage is applied.
The advantage of the aforementioned variable focus lens adopting fluid is that its size can be further reduced than a mechanical lens system that adjusts focal length through mechanical actuation of lenses.
However, the conventional variable focus lens has drawbacks as illustrated in FIG. 4. As the variable focus lens contains fluids, if the fluids are not properly sealed, bubbles or voids 18 may be built up inside the chamber 5 as shown in FIG. 4.
In order to prevent it, the lens may be assembled in the fluid. However, even this does not completely prevent bubble built-up but degrades workability thereby hindering mass production.